This invention is generally directed to novel squaraine compositions, which can be selected for incorporation into layered photoresponsive devices. Thus, the present invention is directed to novel squaraine compositions of matter, these compositions being useful as photoconductive materials in layered photoresponsive devices, especially those devices containing diamine hole transport layers. The layered photoresponsive imaging devices involved, are the subject matter of a related co-pending application wherein it is disclosed that the sensitivity of such devices can be varied or enhanced, allowing the device to be capable of being responsive to visible light, and infrared illumination needed for laser printing. Accordingly, a layered photoresponsive device containing the novel squaraine compositions of the present invention can function so as to enhance or reduce the intrinsic properties of a charge carrier photogenerating material contained therein, in the infrared and/or visible range of the spectrum, thereby allowing this device to be sensitive to either visible light and/or infrared wavelengths.
The use of certain squaraine pigments in photoresponsive imaging devices is known, reference, for example, the disclosure contained in a copending application wherein there is described an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for this device there can be selected various squaraine pigments, including hydroxy squaraine compositions of the formula as outlined on page 13, beginning at line 21 of the co-pending application. Moreover, there is disclosed in U.S. Pat. No. 3,824,099, certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
The formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known, one such method involving the formation of an electrostatic latent image on the surface of a photosensitive plate, referred to in the art as a photoreceptor. This photoreceptor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive insulating material, and in many instances, a thin barrier layer is situated between the substrate and the photoconductive layer in order to prevent undesirable charge injection.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device, containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described for example, in U.S. Pat. No. 3,121,006, wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. In a commercial form there is coated on a paper backing a binder layer containing particles of zinc oxide uniformly dispersed in a resinous binder. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result the photoconductive particles must be in a substantially contiguous particle to particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, with the uniform dispersion of photoconductive particles described a relatively high volume concentration of photoconductor material, about 50 percent by volume, is usually necessary in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. This high photoconductive loading can result in destroying the physical continuity of the resinous binder, thus significantly reducing the mechanical properties thereof. Illustrative examples of specific binder materials disclosed in this patent include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor materials comprised of inorganic or organic materials wherein the charge carrier generating, and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain higher quality images. Also, there is desired layered photoresponsive devices which are responsive to visible light, and/or infrared illumination needed for laser printing.
Recently, there has been disclosed other layered photoresponsive devices including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium, and phthalocyanines, while examples of transport layers include certain diamines as mentioned herein. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990 and 4,251,612 are totally incorporated herein by reference.
Many other patents are in existence describing photoresponsive devices including layered devices containing generating substances, such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging the member, with an electrostatic charge of a first polarity, and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity, which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer such as by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image, is present across the photoconductive layer and the overcoating layer.
There is also disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting the carriers into a continuous active layer containing an organic transporting material which is substantially non-absorbing in the spectral region of intended use, but which is active in that it allows the injection of photogenerated holes from the photoconductive layer and allows these holes to be transported through the active layer. Additionally, there is disclosed in U.S. Pat. No. 3,041,116, a photoconductive material containing a transparent plastic material overcoated on a layer of vitreous selenium contained on a substrate.
Furthermore, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383, photoresponsive imaging members comprised of trigonal selenium doped with sodium carbonate, sodium selenite, and trigonal selenium doped with barium carbonate and barium selenite.
While photoresponsive devices containing the above-described known squaraine materials are suitable for their intended purposes, there continues to be a need for the development of improved devices, particularly layered devices, containing novel squaraine materials. Additionally, their continues to be a need for novel squaraine materials which when selected for layered photoresponsive imaging devices allow the generation of acceptable images, and wherein such devices can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Moreover, their continues to be a need for improved layered imaging members wherein the materials selected for the respective layers are substantially inert to users of such devices. Furthermore, their continues to be a need for overcoated photoresponsive devices which are sensitive to a broad range of wavelengths, and more specifically are sensitive to infrared light, and visible light, thereby allowing such devices to be used in a number of imaging and printing systems. Additionally, there continues to be a need for improved photoresponsive devices which can be prepared with a minimum number of processing steps, and wherein the layers are sufficiently adhered to one another to allow the continuous use of such devices in repetitive imaging and printing systems. Also, there continues to be a need for new squaraine compositions, which can be used as photoconductive substances in layered photoresponsive devices.